Glass fibers have been commonly incorporated in thermoplastic molded and other cured plastics for added strength and durability. These molded plastic parts have been successfully adapted for many applications and are commonly molded into automotive interior trim parts such as instrument panel substrates and exterior bumper facades. The glass fiber is introduced in a mold where resinous plastic is then injected such that the glass fibers become imbedded into the final formed object.
It is now common to incorporate the glass fibers into a preform and then place the preform into the mold. The preform is made from chopped glass fibers of a desired length with the fibers sprayed or blown onto a porous overform. The glass fibers are secured in place against the porous overform via a vacuum applied through the screen. Immediately following the fiber placement, a binder agent is often sprayed on the fibers and allowed to cure which sets the fibers in place in the preform.
It is also known that if fibers are oriented along a longitudinal direction, the strength and rigidity of the finished article along the longitudinal direction is increased while providing relative flexure along the transverse direction. The amount of orientation obtained during a spray process of the fibers has been nominal. Up to now, increased orientation has been obtained through more expensive application methods such as laying down of the fibers or using a premade mat of fibers.
The preform shape may vary and range form a simple channel shape to a complex shape with many curves and vertical wall sections. Even with the vacuum applied onto the preform overform, the fibers may sag along any vertical wall section due to the force of gravity. The sag can be worse at longer vertical extending sections. Any sag of the preform is undesirable in that the sag causes loss of strength and structural integrity.
What is needed is a method for eliminating sag of the fibers on the vertical sections of the preform screen while providing an expeditious method for orienting the fibers on the vertical section of an overform.